Method and circuitry for detecting faults in field oriented controlled permanent magnet synchronous machines

ABSTRACT

A system includes a proportional-integrated-derivative (PID) regulator. The system also includes a fault detection unit. The fault detection unit is for receiving at least two outputs from the PID regulator. The at least two outputs include at least two rotor reference frame (D-Q) currents. The fault detection unit is further for generating a detection signal based on the at least two rotor reference frame currents. The detection signal identifies a fault based on the fault detection signal amplitude value based on the magnitudes of the amplitudes for each of the at least two rotor reference frame D-Q currents. The fault detection unit is for identifying an existence of a permanent magnet motor fault based on a comparison between the fault detection signal amplitude value and an amplitude threshold value. Further the fault localization signature is utilized to locate the location of the fault.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/508,840 filed Oct. 7, 2014, which is incorporated herein by referencein its entirety.

BACKGROUND

This relates generally to electronic circuitry, and more particularly todetecting faults in field oriented controlled (FOC) permanent magnetsynchronous machines (PMSM) and drives.

Electric machines are utilized in a range of applications includingindustrial applications, household appliances, automotive pumps andfans, and aerospace applications. Most of such applications require safeand reliable operation of the machine and any associated drive system.Faults in an electric machine can occur for numerous reasons, includingmechanical vibration, thermal cycling, thermal shock, manufacturingdefects and improper maintenance. Detection of electric machine faultscan prevent damage to the machine, the drive electronics, personnel, andother equipment.

SUMMARY

In a first example, a system is provided. The system includes aproportional-integral-derivative (PID) regulator. The system alsoincludes a fault detection unit. The fault detection unit is forreceiving at least two outputs from the PID regulator. The at least twooutputs include at least two rotor reference frame currents (D-Qcurrents). The fault detection unit is also for determining a magnitudeof an amplitude for each of the at least two rotor reference framecurrents. The fault detection unit is further for generating a detectionsignal based on the at least two rotor reference frame currents. Thedetection signal identifies a single amplitude magnitude value based onthe magnitudes of the amplitudes for each of the at least two rotorreference frame currents. The fault detection unit is for identifying anexistence of a permanent magnet motor/drive fault based on a comparisonbetween the fault detection signal magnitude value and a pre-definedthreshold value.

In a second example, a fault detection unit is provided. The faultdetection unit includes a threshold detector for receiving at least twooutputs from a proportional-integral-derivative (PID) regulator and fordetermining a magnitude of an amplitude for each of the at least tworotor reference frame currents. The at least two outputs include atleast two rotor reference frame currents. The fault detection unit alsoincludes a detection signal generation unit for generating a detectionsignal based on the at least two rotor reference frame currents. Thedetection signal identifies a single amplitude magnitude value based onthe magnitudes of the amplitudes for each of the at least two rotorreference frame currents. The fault detection unit further includes acomparator for comparing the signal magnitude value with a presetthreshold value to identify an existence of a permanent magnet motorfault.

In a third example, a method is provided. The method includes receivingat least two outputs from a proportional-integral-derivative (PID)regulator and for determining a magnitude of an amplitude for each ofthe at least two rotor reference frame currents. The at least twooutputs include at least two rotor reference frame currents. The methodalso includes determining a magnitude of an amplitude for each of the atleast two rotor reference frame currents. The method further includesgenerating a detection signal based on the at least two rotor referenceframe currents. The detection signal identifies a fault based on themagnitude value of the signal for each of the at least two rotorreference frame currents. The method includes identifying an existenceof a permanent magnet motor/drive fault based on a comparison betweenthe signal amplitude value and the preset threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example block diagram of a system with a field orientedcontrolled (FOC) permanent magnet synchronous machine (PMSM) accordingto this disclosure;

FIG. 2 is an example block diagram of a system for detecting faults inFOC PMSM machines and drives according to this disclosure;

FIG. 3A is an example diagram of a D-Q current signature (rotorreference frame current signature) according to this disclosure;

FIG. 3B is an example diagram of a phase current signature according tothis disclosure;

FIG. 4 is an example block diagram of a fault detection unit accordingto this disclosure; and

FIG. 5 is a flow diagram of an example fault detection method accordingto this disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Electric machines are utilized in a range of applications includingindustrial applications, household appliances, automotive traction,pumps and fans, and aerospace applications. Most of such applicationsrequire safe and reliable operation of the machine and any associateddrive system. Faults in an electric machine can occur for numerousreasons, including mechanical vibration, thermal cycling, thermal shock,manufacturing defects and improper maintenance. Applications ofpermanent magnet synchronous machines (PMSMs) are proliferating due topower density, efficiency gains, and simplicity in control algorithms.Field Oriented Control (FOC) is one control algorithm applied towardsthe control of PMSMs due to simplicity. Some typical faults that canoccur in a PMSM drive system are listed below.

TABLE 01 PMSM Machine Drive System Failure Modes Machine Fault DriveFault Bearing Failure Switch Failure Winding failure (within a phase)Single leg failure Winding failure (between phases) Multiple phasefailure Magnet failure Switch short to phase Open phase fault Switchshort to ground

A winding short in a rotating PMSM is essentially a loop of conductorrotating in a magnetic field. The conductor loop is induced with avoltage generating a current flow in a low resistance path. Currentsbeyond the rated current for the winding can circulate in the loop ofthe conductor even at low speeds due to low resistance. Exceeding therated current of the winding can cause overheating of the machine andcan lead to potentially harmful circumstances. The immediate detectionof a winding fault will prevent damage to the machine, the driveelectronics, personnel, and other equipment.

FIG. 1 is an example block diagram of a system, indicated generally at100, with a field oriented controlled (FOC) permanent magnet synchronousmachine (PMSM) according to this disclosure. As shown in FIG. 1, thesystem 100 includes a rotor reference frame current regulation schemeand I_(dq) to V_(dq) converter unit 102 (hereinafter the RC unit 102), arotor reference frame voltage form (V_(dq)) to phase voltage form(V_(abcs)) transformation unit 101 (hereinafter line voltage to phasevoltage transformation unit 101), a pulse-width-modulation (PWM)generation unit 108, an inverter 104, a permanent magnet motor 106, DCmachine or any mechanism for loading 107 (hereinafter machine 107), anda proportional-integral-derivative (PID) regulator 103. The PIDregulator 103 includes an error calculation unit 110. The system alsoincludes a Clark and Park (CP) transformation unit 112.

The RC unit 102 receives two line current forms (I_(dq)) and convertsthe two line current forms to two rotor reference frame voltage forms(V_(dq)). The RC unit 102 transmits the two rotor reference framevoltage forms to the rotor reference frame voltage to phase voltagetransformation unit 101. The rotor reference frame voltage to phasevoltage transformation unit 101 converts the two rotor reference framevoltage forms to a phase voltage form (V_(abcs)). The phase voltage formis supplied to the PWM generation unit 108. The PWM generation unit 108controls the width of the pulse, formally the pulse duration, based onmodulator signal information.

The inverter 104 receives the phase voltage form from the PMW generationunit 108 and converts the direct current (DC) power into alternatingcurrent (AC) power. In this example, the inverter 104 represents athree-phase inverter that converts DC power into three-phase AC powerwhich is provided to the motor 106. The inverter 104 includes anysuitable structure for converting power from DC form to AC form. Forexample, the inverter 104 could include one or more transistor switchesdriven using pulse width modulation (PWM) signals.

The motor 106 represents a permanent magnet motor that operates usingthe voltages provided by the inverter 104. The motor 106 includes arotor with magnets embedded in or connected to the rotor. The motor 106also includes a stator with multiple teeth around which conductivewindings are wound. The windings are selectively energized andde-energized based on the signals from the inverter 104, which creates arotating magnetic field that causes the rotor to rotate. The motor 106drives a machine 107. The motor can drive the machine 107 with, forexample, a drive shaft and one or more gears.

The system 100 further includes a proportional-integral-derivative (PID)regulator 103. In an embodiment, the PID regulator 103 is aproportional-integral (PI) regulator. The controller includes a PIDregulator 103 with an error calculation unit 110 and a Clark and Park(CP) transformation unit 112. The CP transformation unit 112 receivesbalanced three-phase AC currents from the inverter 104 in the statorreference frame and converts the balanced three-phase AC currents in thestator frame into two currents in the rotor reference frame (I_(g) andI_(d), Q and D axis currents). The CP transformation unit 112 transmitsthe two line currents to the error calculation unit 110. The errorcalculation unit 110 adjusts the two line currents which aresubsequently fed to the RC unit 102.

The RC unit 102, the rotor reference frame voltage to phase voltagetransformation unit 101, and the PWM generation unit 108 togethercontrol the operation of the inverter 104 to thereby control theoperation of the motor 106. For example, the PWM generation unit 108generates PWM signals that drive the transistor switches in the inverter104. By controlling the duty cycles of the PWM signals, the PWMgeneration unit 108 controls the three-phase voltages provided by theinverter 104 to the motor 106.

In this example, the RC unit 102 receives as input a commanded speedsignal w*, which identifies a desired speed of the motor 106. The RCunit 102 also receives as input feedback from the PID regulator 103where the feedback identifies the estimated motor speed, rotor position,or other characteristic(s) of the motor 106. The PWM generator 108 usesthe inputs to generate PWM signals for driving the transistor switchesin the inverter 104.

Although FIG. 1 illustrates one example of a system 100 with a fieldoriented controlled (FOC) permanent magnet synchronous machine (PMSM),various changes can be made to FIG. 1 without departing from the scopeof this disclosure. For example, various components in FIG. 1 can becombined or further subdivided. As a particular example, one or more ofthe components 101, 102, 104, and 108 could be incorporated into themotor 106 itself.

FIG. 2 is an example block diagram of a system, indicated generally at200, for detecting faults in field oriented controlled (FOC) permanentmagnet synchronous machines (PMSMs) according to this disclosure. Asshown in FIG. 2, the system 200 includes an RC unit 202, a rotorreference frame voltage to phase voltage transformation unit 201, a PWMgeneration unit 208, an inverter 204, a permanent magnet motor 206, amachine 207, and a PID regulator 203. The PID regulator 203 includes anerror calculation unit 210 and a Clark and Park (CP) transformation unit212. Each of these components of system 200 are the same as or aresimilar to the corresponding RC unit 102, line voltage to phase voltagetransformation unit 101, PWM generation unit 108, inverter 104,permanent magnet motor 106, machine 107, and PID regulator 103 includingthe error calculation unit 110 and the CP transformation unit 112illustrated in FIG. 1.

The system 200 also includes a fault detection unit 214. The faultdetection unit 214 detects an existence of a fault in the permanentmagnet motor 206 by executing a detection algorithm based on a rotorreference frame current signature (D-Q current signature) due to machineimbalance caused by the fault. For example, for control purposes, anelectric machine is considered a balanced three phase machine. An FOCalgorithm relies on a balanced machine that is controlled with abalanced set of three phase currents. When the CP transformation unit212 is activated, balanced three phase currents in the stator referenceframe transform into two DC like signals (non-sinusoidal) in the rotorreference frame. Each of the two DC signals is in a steady state afterthe transient period.

If a fault exists, the three phase currents will be unbalanced duringsteady state operation and the CP transformation unit 212 does notproduce two DC signals in the rotor reference frame that are in a steadystate. In this case, an unbalanced motor has rotor reference framecurrents with a sinusoidal component superimposed on the DC component.The fault detection unit 214 identifies the sinusoidal componentsuperimposed on the DC component and determines that a fault exists, forexample based on an amplitude value of the sinusoidal component.

FIG. 3A is an example diagram of a D-Q current according to thisdisclosure. An analogous variation is reflected on the PID controllererror output and control signal output, which are being utilized forfault diagnostic and localization. The fault detection unit 214 detectsthe existence of faults. For example, as shown in FIG. 3A, the faultdetection unit 214 receives a plurality of D-Q current values over aperiod of time producing a D-Q current signature. From the 0.48 secondmark up to the 0.5 second mark, the fault detection unit 214 determinesthat the motor and the phase currents are balanced as the D-Q currentsignature is in a steady state. At the 0.5 second mark, the D-Q currentsignature changes from a steady state current to sinusoidal currents.The rotor reference frame PID regulator outputs are also affected by thesinusoidal currents. The fault detection unit 214 determines that themotor and the phase currents are out of balance as the D-Q currenterrors are not in a steady state, thus indicating the existence of afault.

FIG. 3B is an example diagram of a phase current signature according tothis disclosure. The fault detection unit 214 derives the D-Q currentsignature from the phase current signature, for example after the faultdetection unit 214 determines the existence of a fault. The derived D-Qcurrent signature has the same or similar phase current signatureprovided to the motor 206 from the inverter 204. By deriving the D-Qcurrent signature from the phase signature, the fault detection unit 214can identify the type of fault. For example, the derived D-Q currentsignature illustrated in FIG. 3A follows the phase current signatureillustrated in FIG. 3B. As illustrated in FIG. 3B, from the 0.48 secondmark up to the 0.5 second mark, the derived phase current signatureillustrates three sinusoidal current signatures (phases A, B, and C)with the same or similar amplitudes reflecting the steady state D-Qcurrent signature within the same time frame. At the 0.5 second mark,the phase current signature changes so that the phase B currentsignature has zero amplitude while the phase A and phase C currentsignatures have increasing amplitudes reflecting the fault conditionidentified using the sinusoidal D-Q current signature of FIG. 3A.

D-Q currents and the rotor position together are utilized to locate thelocation of fault occurrence. The rotor position can be estimated oracquired via a rotor position sensor. For example, a particularconfiguration or pattern of the phase current signature can identifyswitch failures, single leg failures, switch open failures, switch shortto ground failures, and the like. Based on the identifications of faulttypes, the fault detection unit 214 can determine a location of thefault.

Additionally the fault detection unit 214 uses an algorithm to detectthe faulty phase. A faulty phase identification scheme is based on thephase shift induced in the function ‘ƒ’, with respect to the actualrotor position due to the fault condition. The derivation is as followsassuming a fault on phase ‘C’.

$\begin{matrix}{i_{qs}^{r} = {\frac{2}{3}\left\lbrack {{{\cos(\theta)}i_{as}} + {{\cos\left( {\theta - \frac{2\;\pi}{3}} \right)}i_{bs}} + {{\cos\left( {\theta - \frac{4\;\pi}{3}} \right)}i_{cs}}} \right)}} & {{Eq}.\mspace{14mu}(1)} \\{i_{qs}^{r} = {\frac{2}{3}\left\lbrack {{{\cos(\theta)}i_{as}} - {{\cos\left( {\theta - \frac{2\;\pi}{3}} \right)}i_{as}}} \right\rbrack}} & {{Eq}.\mspace{14mu}(2)} \\{i_{qs}^{r} = {\frac{- 2}{\sqrt{3}}\left\lbrack {i_{as}{\sin\left( {\theta - \frac{\pi}{3}} \right)}} \right\rbrack}} & {{Eq}.\mspace{14mu}(3)} \\{i_{ds}^{r} = {\frac{2}{3}\left\lbrack {{{\sin(\theta)}i_{as}} + {{\sin\left( {\theta - \frac{2\;\pi}{3}} \right)}i_{bs}} + {{\sin\left( {\theta - \frac{4\;\pi}{3}} \right)}i_{cs}}} \right)}} & {{Eq}.\mspace{14mu}(4)} \\{i_{ds}^{r} = {\frac{2}{3}\left\lbrack {{{\sin(\theta)}i_{as}} - {{\sin\left( {\theta - \frac{2\;\pi}{3}} \right)}i_{as}}} \right\rbrack}} & {{Eq}.\mspace{14mu}(5)} \\{i_{ds}^{r} = {\frac{2}{\sqrt{3}}\left\lbrack {i_{as}{\cos\left( {\theta - \frac{\pi}{3}} \right)}} \right\rbrack}} & {{Eq}.\mspace{14mu}(6)} \\{f = {\frac{i_{qs}^{r}}{i_{ds}^{r}} = {- {\tan\left( {\theta - \frac{\pi}{3}} \right)}}}} & {{Eq}.\mspace{14mu}(7)}\end{matrix}$

If the actual electrical angle is known, the phase shift in the abovesignal ‘ƒ’ can be extracted. The phase shift will indicate the faultywinding/phase.

${\angle\; f} = {{\angle\left( {\theta_{electrical}(t)} \right)} - {\angle\left( {\tan^{- 1}\left( \frac{- {i_{{qs}\_{error}}^{r}(t)}}{i_{{ds}\_{error}}^{r}(t)} \right)} \right)}}$

Although FIG. 2 illustrates one example of a system 200 for detectingfaults in field oriented controlled (FOC) permanent magnet synchronousmachines (PMSMs), various changes can be made to FIG. 2 withoutdeparting from the scope of this disclosure. For example, variouscomponents in FIG. 2 can be combined or further subdivided. As aparticular example, one or more of the components 201, 202, 204, and 208could be incorporated into the motor 206 itself.

FIG. 4 is an example block diagram of a fault detection unit 414according to this disclosure. The design details of the fault detectionunit 414 could be incorporated into the fault detection unit 214 in thesystem 200 of FIG. 2. Of course, these design details could beincorporated into other fault detection units operating in othersystems. As shown in FIG. 4, the fault detection unit 414 includes athreshold detector 416, a detection signal generation unit 418, acomparator 420, a fault counter 422, and detection threshold storageunit 424.

The threshold detector 416 receives at least two outputs from aproportional-integral-derivative (PID) regulator (such as PID regulator203 of FIG. 2). The at least two outputs include at least two rotorreference frame D-Q current signatures. The threshold detector 416determines a magnitude of an amplitude for each of the at least tworotor reference frame D-Q currents in order to enable the faultdetection circuit. For example, when the motor 206 is balanced, thethreshold detector 416 will determine that the magnitude of the each ofthe at least two rotor reference frame D-Q currents is a value equal tozero or close to zero, as the rotor reference frame currents are insteady state. When the motor 206 is not balanced, the threshold detector416 will determine that the magnitude of the amplitude for each of theat least two rotor reference frame D-Q currents is a value significantlygreater than zero, as the rotor reference frame currents are not in asteady state. After the at least two rotor reference frame D-Q currentsignatures pass through the threshold detector 416, the at least tworotor reference frame D-Q current signatures are received by thedetection signal generation unit 418.

The detection signal generation unit 418 receives the at least two rotorreference frame D-Q current signatures and generates a detection signalbased on the at least two rotor reference frame D-Q current signatures.That is, the detection signal is a single signal that is a combinationof the D current signature and the Q current signature. The detectionsignal identifies a single amplitude magnitude value from a singlesignal based on the magnitudes of the amplitudes for each of the atleast two rotor reference frame D-Q current signatures. The detectionsignal generation unit 418 calculates the single amplitude magnitudevalue to provide an accurate amplitude magnitude value. The detectionsignal generation unit 418 can generate a detection signal using thefollowing equation:

I_(d_error)^(x)/(I_(d_error)^(x) + I_(q_error)^(x));  x = 1, 2, 3, . . .

After the detection signal generation unit 418 generates the detectionsignal, the detection signal generation unit 418 transmits the detectionsignal to the comparator 420.

The comparator 420 receives the detection signal and compares the singleamplitude magnitude value of the detection signal with an amplitudethreshold value to identify an existence of a permanent magnet motorfault. For example, if the single amplitude magnitude value is greaterthan the amplitude threshold, then a fault exists. The detectionthreshold storage unit 424 stores the amplitude threshold value andprovides the amplitude threshold value to the comparator 420 for signalcomparisons.

The fault detection unit 414 also includes a fault counter 422. Thefault counter 422 verifies that a fault exists. For example, afterdetermining that a first fault exists, the fault counter 422 counts thenumber of subsequent fault signal threshold crossings that are detectedat the comparator 420. When the fault counter 422 detects apredetermined quantity of subsequent faults, the fault counter 422verifies that the fault exists. The fault counter 422 can verify that afault exists after detecting at least one subsequent fault. The faultcounter 422 can verify that a fault exists after a predeterminedquantity of faults is detected within a predetermined period of time.The fault counter 422 can verify that a fault exists when apredetermined quantity of consecutive faults signal threshold crossingsare detected within a predetermined period of time. The fault counter422 can verify that a fault exists when a percentage of faults versusnon-faults are detected within a predetermined period of time.

FIG. 5 is a flow diagram of an example fault detection method 500according to this disclosure. At step 502, a fault detection unit 414receives at least two outputs or output streams from aproportional-integral-derivative (PID) regulator. The at least twooutputs include at least two rotor reference frame currents or currentsignatures. At step 504, the fault detection unit 414 determines amagnitude of an amplitude of each of the at least two rotor referenceframe currents. At step 506, the fault detection unit 414 generates adetection signal based on the at least two rotor reference framecurrents. The detection signal identifies a single amplitude magnitudevalue based on the magnitudes of the amplitudes for each of the at leasttwo rotor reference frame currents. At step 508, the fault detectionunit 414 identifies the existence of a fault based on a comparisonbetween the single amplitude magnitude value and an amplitude thresholdvalue. For example, the fault detection unit 414 can compare the singleamplitude magnitude value with an amplitude threshold value anddetermine if a fault exists based on the comparison. At step 510, thefault detection unit 414 verifies the existence of the permanent magnetmotor fault by comparing a predetermined quantity of subsequent singleamplitude magnitude values with the amplitude threshold value.

Although FIG. 5 illustrates one example of a fault detection method 500,various changes may be made to FIG. 5. For example, while FIG. 5illustrates a series of steps, various steps in each figure couldoverlap, occur in parallel, occur in a different order, or occur anynumber of times. Also, one or more of the steps of the method 500 couldbe removed, or other steps could be added to the method 500. Moreover,while the method 500 is described as being performed by the faultdetection unit 414, the method 500 could be performed by any othersuitable unit, device, or system.

In some embodiments, various functions described above are implementedor supported by a computer program that is formed from computer readableprogram code and that is embodied in a computer readable medium. Thephrase “computer readable program code” includes any type of computercode, including source code, object code, and executable code. Thephrase “computer readable medium” includes any type of medium capable ofbeing accessed by a computer, such as read only memory (ROM), randomaccess memory (RAM), a hard disk drive, a compact disc (CD), a digitalvideo disc (DVD), or any other type of memory. A “non-transitory”computer readable medium excludes wired, wireless, optical, or othercommunication links that transport transitory electrical or othersignals. A non-transitory computer readable medium includes media wheredata can be permanently stored and media where data can be stored andlater overwritten, such as a rewritable optical disc or an erasablememory device.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “application”and “program” refer to one or more computer programs, softwarecomponents, sets of instructions, procedures, functions, objects,classes, instances, related data, or a portion thereof adapted forimplementation in a suitable computer code (including source code,object code, or executable code). The terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation. The term“or” is inclusive, meaning and/or. The phrase “associated with,” as wellas derivatives thereof, may mean to include, be included within,interconnect with, contain, be contained within, connect to or with,couple to or with, be communicable with, cooperate with, interleave,juxtapose, be proximate to, be bound to or with, have, have a propertyof, have a relationship to or with, or the like. The phrase “at leastone of,” when used with a list of items, means that differentcombinations of one or more of the listed items may be used, and onlyone item in the list may be needed. For example, “at least one of: A, B,and C” includes any of the following combinations: A, B, C, A and B, Aand C, B and C, and A and B and C.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. A system comprising: aproportional-integral-derivative (PID) regulator circuit having firstand second rotor reference frame current outputs adapted to be coupledto a permanent magnet motor; and a fault detection circuit including athreshold detector circuit, a signal detector and a comparator; thethreshold detector circuit having: first and second inputs respectivelycoupled to the first and second rotor reference frame current outputs;and an amplitude magnitude output; the signal detector having: an inputcoupled to the amplitude magnitude output; and a detection output; thecomparator having: a first input coupled to the detection output; asecond input coupled to an amplitude threshold node; and, a comparatoroutput; the comparator configured to: compare a signal at the detectionoutput to a signal at the amplitude threshold node; and responsive tothat comparison, output a comparison signal at the comparator output,the comparison signal indicative of whether a fault exists in a statorwinding of the permanent magnet motor; a signal at the first rotorreference frame current output having a D-axis current value, and asignal at the second rotor reference frame current output having aQ-axis current value; and the signal at the detection output having avalue equal to a magnitude of the D-axis current divided by a sum ofmagnitudes of the D-axis current and the Q-axis current.
 2. The systemof claim 1, wherein the signal at the detection output has a singleamplitude magnitude value.
 3. The system of claim 1, wherein the faultdetection circuit includes a fault counter having an input coupled tothe comparator output, the fault counter configured to count a number ofinstances in which the comparison signal indicates that the faultexists.
 4. The system of claim 3, wherein the fault detection circuit isconfigured to verify the fault, responsive to at least a particularnumber of the instances being counted by the fault counter.
 5. Thesystem of claim 1, wherein the fault detection circuit is configured to:derive a three-phase stator reference frame current from the first andsecond rotor reference frame current outputs, after a particular numberof instances in which the comparison signal indicates that the faultexists; and determine a drive fault type based on the three-phase statorreference frame current.
 6. The system of claim 5, wherein the drivefault type includes at least one of: a switch failure fault, a singleleg failure, a multiple phase failure, a switch open fault, a switchshort to phase fault, or a switch short to ground fault.
 7. The systemof claim 5, wherein the fault detection circuit is configured toidentify a permanent magnet motor fault type based on the drive faulttype, and the permanent magnet motor fault type includes at least oneof: a bearing failure, a winding failure within a phase, a windingfailure between phases, a magnet failure, or an open phase fault.
 8. Thesystem of claim 1, wherein the PID regulator circuit is a component of afield oriented control (FOC) permanent magnet synchronous machine(PMSM).
 9. A fault detection circuit comprising: a threshold detectorcircuit having: first and second inputs adapted to be respectivelycoupled to first and second rotor reference frame current outputs of aregulator circuit; and an amplitude magnitude output; a signal detectorhaving: an input coupled to the amplitude magnitude output; and adetection output; and a comparator having: a first input coupled to thedetection output; a second input coupled to an amplitude threshold node;and a comparator output; the comparator configured to: compare a signalat the detection output to a signal at the amplitude threshold node; andresponsive to that comparison, output a comparison signal at thecomparator output, the comparison signal indicative of whether apermanent magnet motor fault exists; a signal at the first rotorreference frame current output having a D-axis current value, and asignal at the second rotor reference frame current output having aQ-axis current value; and the signal at the detection output having avalue equal to a magnitude of the D-axis current divided by a sum ofmagnitudes of the D-axis current and the Q-axis current.
 10. The faultdetection circuit of claim 9, wherein: the signal at the detectionoutput has a single amplitude magnitude value; and responsive to thesingle amplitude magnitude value being greater than a value of thesignal at the amplitude threshold node, the comparison signal indicatesthat the permanent magnet motor fault exists.
 11. The fault detectioncircuit of claim 10, further comprising a counter having an inputcoupled to the comparator output, the counter configured to count anumber of instances in which the comparison signal indicates that thepermanent magnet motor fault exists; the fault detection circuitconfigured to verify the permanent magnet motor fault, responsive to atleast a particular number of the instances being counted by the counter.12. The fault detection circuit of claim 9, wherein the permanent magnetmotor fault is a stator winding fault.
 13. The fault detection circuitof claim 9, wherein the fault detection circuit is configured to: derivea three-phase stator reference frame current from the first and secondrotor reference frame current outputs, after a particular number ofinstances in which the comparison signal indicates that the permanentmagnet motor fault exists; and determine a drive fault type based on thethree-phase stator reference frame current.
 14. The fault detectioncircuit of claim 13, wherein the drive fault type includes at least oneof: a switch failure fault, a single leg failure, a multiple phasefailure, a switch open fault, a switch short to phase fault, or a switchshort to ground fault.
 15. The fault detection circuit of claim 13,wherein the fault detection circuit is configured to identify apermanent magnet motor fault type based on the drive fault type, and thepermanent magnet motor fault type includes at least one of: a bearingfailure, a winding failure within a phase, a winding failure betweenphases, a magnet failure, or an open phase fault.